Dry electrolytic condenser



Oct. 31, 1939. J. M. BOOE ET AL DRY ELECTROLYTIC CONDENSER Filed Oct.12, 1937 Patented Oct. 31, 1939 UNITED STATES PATENT OFFICE DRYELECTROLYTIC CONDENSER Application October 12, 1937, Serial No. 168,542

4 Claims.

This invention relates to dry electrolytic condensers.

An object of the invention is to improve dry electrolytic condensers andelectrodes therefor.

Other objects of the invention will be apparent from the followingdescription and accompanying drawing taken in connection with theappended claims.

The invention comprises the features of construction, combination ofelements, arrangement of parts, and methods of manufacture and operationreferred to above or which will be brought out and exemplified in thedisclosure hereinafter set forth, including the illustrations in thedrawing.

In the drawing:

Figure 1 shows one method of preparing improved electrodes for dryelectrolytic condensers;

Figure 2 illustrates a completed electrode;

Figure 3 shows a partly assembled dry electrolytic condenser embodyingthe electrode; and

Figure 4 shows a complete condenser assembly.

According to the present invention a dry electrolytic condenser isprovided having a flexible electrode formed of cloth upon which afilmforming metal has been deposited in cohering finely divided form, bysuch a method as a metal spray process.

While a preferred embodiment of the invention is described herein, it iscontemplated that considerable variation may be made in the method ofprocedure and the construction of parts without departing from thespirit of the invention. In the following description and in the claims,parts will be identified by specific names for convenience, but they areintended to be as generic in their application to similar parts as theart will permit.

Referring to the drawing Figure 1 shows a method of forming the flexibleelectrode which comprises leading a strip of cloth Ill over a roller l land simultaneously spraying a deposit of filmfcrming metal, such asaluminum, onto it by a Schoop spray gun l2. If desired, but notnecessarily, the cloth can then be sprayed on the opposite face bySchoop gun l3 as it is led over a second roller 14.

The cloth used should preferably be a relatively loose woven open meshfabric of loose-twisted threads so that the sprayed metal can penetratebetween the threads and hence be distributed throughout a considerableproportion of the cloth layer. The surface area of the sprayed metal ismade very great not only because of the inherent porous nature ofsprayed metal consisting of finely divided particles bonded together butalso because of the lattice work of the gauze or cloth and the contourand spacing of the cloth fibres among which the metal particles areinterspersed.

Many varieties of cloth or gauze can be used. Muslin, cheesecloth,cotton gauze and the like are especially suitable in the various weightsand thread spacing obtainable commercially. The cloth should preferablybe bleached and unsized and free of impurities such as chlorides. Anadvantage of cloth as a base is that it is readily obtainable in pureform.

The spraying time and density are preferably regulated so as to producea sheet which is porous and flexible enough to roll without cracking butin which the sprayed metal particles are bonded together suificiently toconduct electricity throughout the sheet, even after filmformation. Inthe preferred embodiment it will be found desirable to use cloth ofrelatively open mesh and to regulate the spraying so as to leave quite afew pin-holes through which it is possible to perceive light when theelectrode sheet is held up before a light source.

The film-formation may be carried out by conventional methods known tothe electrolytic condenser art such as by passing the electrode througha solution of borax and boric acid and passing a uni-directionalelectric current between the electrode and the solution.

Figure 2 shows a completed electrode l8 comprising a length of cloth l0sprayed with aluminum I5, as described. A suitable terminal I6 issecured to the electrode by laying it along the edge and punching holesll through the assembly to provide interlocking portions.

Figure 3 shows a dry electrolytic condenser partly assembled andcomprising electrode [8 as anode and a co-operating ioil cathode I9having a terminal 23 interspaced with electrolyte permeable sheetspacers 2|] and 2|, such as paper, cloth, regenerated sheet cellulose orthe like and wound on a mandrel 22.

The condenser is impregnated with a viscous film-maintaining electrolyteof the type used in dry electrolytic condensers. A suitable electrolytecomprises:

Boric acid ounces 20 Ammonium hydroxide cc Ethylene glycol cc 640 boiledtogether until the boiling point of the composition reachesapproximately 120 C. to C. depending on the sparking voltage required.An electrolyte of fairly low viscosity and substantially tree fromcrystals at the time of impregnation is most suitable. The viscosityofthe above electrolyte may, in most cases, be between 1 and 3 at 200 1''.as compared with water at 60 1".

However, even more viscous electrolytes can be used. The high porosityof the electrode enables viscous electrolytes to be squeezed through thesheet and into the numerous pores and recesses during impregnation. Inaddition the wicklike nature of the electrode tends to draw up theelectrolyte and hold it within its pores by capillarity.

If the condenser is intended for AC operation it is obvious that asecond electrode similar to II can be used in place of foil l9.

Figure 4 shows a completed condenser comprising the assembly of Figure 3inserted in a can 24 provided with a laminated insulating top 25 havinga central terminal 26 attached to tab it of the condenser. Tab 23 isspun under the edge of the can so that the can serves as the otherterminal.

As an indication of the advantages obtainable by the present inventionit has been found that sprayed aluminum electrodes according to theinvention may have from 10 to 20 times the capacity of plain aluminumfoil electrodes of the prior art. The result is that condensers of agiven capacity can be made in correspondingly smaller sizes or thatcorrespondingly greater capacities can be obtained with the same sizes.

While the present invention, as to its objects and advantages, has beendescribed herein as carried out in specific embodiments thereof, it isnot desired to be limited thereby but it is in tended to cover theinvention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. A flexible sheet electrode for dry electrolytic condensers comprisinga cloth base and finely divided film-forming metal deposited thereon,said metal particles cohering to provide a conductive path along theelectrode layer and said electrode being suillciently open-mesh andporous to permit light to pass through the-electrode layer at amultiplicity of distributed points throughout its 'area.

2. A dry electrolytic condenser comprising two electrodes, a spacer andan electrolyte, one of said electrodes comprising a cloth base andfinely divided film-forming metal deposited thereon, said electrodehaving recesses in the surface thereof resulting from the contours andlattice structure of said cloth base, said metal particles cohering toprovide a conductive path along the electrode layer and said electrodebeing sufficiently open-mesh and porous to permit light to pass throughthe electrode layer at a multiplicity of distributed" points throughoutits area.

3. A dry electrolytic condenser comprising two' electrodes and paperspacers in enrolled form, impregnated with a viscous film formingelectrolyte, one of said electrodes comprising a cloth base andfinely-divided film-forming metal deposited thereon, said electrodehaving recesses in the surface thereof resulting from the contours andlattice structure of said cloth base, said metal particles cohering toprovide a conductive.

path along the electrode layer and said electrode being sufllcientlyopen-mesh and porous to permit light to pass through the electrode layerat a multiplicity of distributed points throughout

